Electronically controlled direct fuel injection devices are well known in the art. Such devices include electronically controlled fuel injectors, which may be hydraulically or mechanically actuated. During an injection event, an electronically controlled fuel injector injects fuel into a combustion chamber in response to an electronic fuel injection signal produced by a controller. This signal includes a waveform indicative of an injection rate. The fuel injection waveform is tailored based on engine operating conditions. Specifically, the fuel injection waveform is tailored to include multiple fuel injections (hereafter “shots”) during each injection event. This use of multiple shots during each injection event may enable compliance with exhaust emissions regulations. These regulations restrict, for example, the emission of hydrocarbons and carbon monoxide, the release of particulates, and the release of nitrogen oxides (NOx). Each shot has specific attributes such as, for example, a duration and an injection rate. Shots are grouped, ordered, and timed to form shot modes, which correspond to fuel injection waveforms. Based on an engine speed and a desired quantity of fuel supplied to the engine, a shot mode is selected for each injection event. At different engine operating conditions, different shot modes are selected to achieve desired engine performances while complying with emissions regulations.
During normal operation of the engine, the selected shot mode may change several times. Typically, shot modes differ slightly in both noise level and torque produced. In some instances, transitioning from one shot mode to another causes a noticeable “step-change” in either or both of these characteristics and/or other characteristics. This sudden change in characteristics is undesirable.
One way to minimize the sudden change in characteristics is described in U.S. Pat. No. 7,051,699 (the '699 patent) issued to McGee et al on May 30, 2006. The '699 patent describes methods for operating a fuel injection system of an engine. Specifically, the methods include operating a first number of fuel injectors in a first mode during a first engine cycle. The first mode has a first set of fuel delivery characteristics, including at least one fuel shot per fuel injector per engine cycle. The methods also include operating a second number of the fuel injectors in a second mode during the first engine cycle. The second mode has a second set of fuel delivery characteristics, including at least one fuel shot per fuel injector per engine cycle.
Although the methods of the '699 patent may lessen the noticeability of a transition between the two modes of the '699 patent, the methods of the '699 patent may do little to dynamically control a rate of transition between the two modes. Failing to dynamically control the rate of transition between the two modes may result in an undesirable tradeoff between transition noticeability and a responsiveness of the engine of the '699 patent. For example, it may sometimes be desirable to minimize the noticeability of the transition between the two modes. This may be best accomplished by a slow transition between the two modes. It may at other times be desirable to maximize the responsiveness of the engine. This may be best accomplished by a fast transition between the two modes.
The disclosed method and system are directed to improving prior systems.